var jQuery = {}

jQuery.ajax = function (url, {
	async = true,
	beforeSend = function () {},
	cache = true,
	complete = function () {},
	crossDomain = false,
	global = true,
  // ... more config 解构赋值时设置的默认值
} = {}) {
	console.log(url, async, crossDomain)
  // ... do stuff
};


console.log(jQuery.ajax, typeof jQuery.ajax)

jQuery.ajax('baidu.com', {
	async: false,
	complete: false,
	crossDomain: "crossDomain"

})